Crossword Genius

Nominally favourite concert piece (5)

Ross

I believe the answer is:

peter

I'm a little stuck... Click here to teach me more about this clue!

'piece' is the definition.
(peter is a kind of piece)

'nominally favourite concert' is the wordplay.
I cannot really see how this works, but
'favourite' could be 'pet' (synonyms) and 'pet' is present in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for peter that I've seen before include "- Grimes (Britten)" , "Lord -- Wimsey (Sayers)" , "Boy's name - safe" , "and 4 across Doctor Who actor" , "' - - Pan' by Barrie" .)

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